The present invention generally relates to mining and excavating tools and, more particularly, is concerned with a cutting bit incorporating erosion resistant structure rearwardly of its hard tip wherein this erosion resistant structure includes a hardfacing material deposited in a channel in the bit body axially rearwardly of the hard tip.
Many mining and excavating tools employ drums and the like on which are mounted a multiplicity of rotary cutting bits. In the course of operating these tools, the bits are forcibly engaged with coal and rock formations to reduce the same and thus are subjected to a high degree of stress and wear. Typically, each bit has a hard, wear resistant, pointed insert or tip, for example, being composed of tungsten carbide, which contacts the formation. However, the hard tip is commonly attached to and supported on a conical head of the bit, composed of a different material, such as carbon steel, which is relatively soft when compared to the hard tip. As the bit tip penetrates and reduces the formation, the portion of the bit head backing the hard tip is also brought into abrasive contact with the formation.
Many different embodiments of bits having this general construction appear in the prior art. Representative of the prior art are the bits disclosed in U.S. Pat. Nos. to Healey et al. (3,356,418), Hansen et al. (3,796,464), McKenry et al. (3,830,321), Elders (3,833,264) and 3,833,265), Kniff et al. (3,841,707 and 3,841,708), Stoltz et al. (4,149,753), Den Besten et al. (4,201,421 and 4,462,638), Wrulich et al. (4,247,150), Hahn (4,470,210) and Emmerich (4,484,783).
One major problem with this general bit construction is that, while the hard tip is enduring these extremely abrasive conditions, its softer backing structure, i.e., the bit head, is eroding away, being washed or eaten away over time by its contact with the formation. Once the bit head has eroded a certain degree, it will break off, taking the hard tip with it. Thus, the useful life of the hard tip of each bit on the drum is dependent on how long the head of the bit can last before breaking off. Although there are a large number of bits on the drum, the number of broken off heads will soon increase to the point where replacement is required. Early replacement increases operating costs due to increased tool downtime and usage of replacement parts and maintenance labor.
Consequently, a need still exists for improvements in bit construction which will extend the life of the bit and thereby reduce operating costs without introducing other new costs in place thereof.